1. Field of the Invention
This invention relates to equipment for driving or ramming and for extracting or hoisting piles and the like, and more particularly to driving and extracting apparatus of the type utilizing a vibrator having a reaction mass disposed freely movably within a hammer frame and alternately exposed on opposite sides to drive pressure, on the one hand, and to spring pressure, on the other hand. Such apparatus is intended to be used for driving piles or pile-like material, such as sections of sheet piling, into the ground by initiating forces acting periodically on the plle material in the longitudinal direction thereof.
2. Description of the Prior Art
Apparatus of this type has already been proposed, e.g., in West German Published Application (DAS) No. 2,732,934. Such apparatus makes use of the centrifugal force of rotating flyweights driven electrically or hydraulically, or of reaction forces of masses moved translationally by hydraulic means. One drawback of this prior art apparatus is that during each cycle, the reaction mass is accelerated and then braked again by the pressure medium. As a result, the effective output is relatively low as compared with the propulsive output. In the drive of the reaction mass by means of the pressure medium alone, i.e., without taking into account the natural frequency of the reaction mass and or the passive masses (hammer frame, clamping device, pile material, and ground), it happens that the active mass moves in the opposite direction from the passive masses prior to the impact. This is not so disturbing in purely vibrational operation, but in striking, a large part of the impact energy is nullified in this way.
Apparatus has also been disclosed, e.g., in Swiss Pat. No. 594,111, in which a mass is mounted on springs and caused to vibrate by means of centrifugal forces, the exciting frequency being approximately the same as the natural frequency of the vibrating mass or being in resonance relation thereto. The mass thus vibrating strikes against a stop fixed to the pile material, and in this way the pile material is, on the one hand, set in motion by vibrations which are transmitted via the spring mounting and, on the other hand, driven into or extracted from the ground by the directed blows. Such equipment has the drawback that the impact frequency can be varied only by reconstructing the apparatus, i.e., by changing the springs and flyweights to a different frequency. Another disturbing factor is that the desired frequency must be one which is harmonic relative to the speed of rotation or the flyweights. At higher harmonic vibrations, the adaptation achieved is very unstable. In driving and extracting work, the energy requirement varies as a function of the depth to which the pile material penetrates into the ground. At shallow depths, it is preferable to work with high-frequency vibration, the noise level also being low in this case. With increasing depth of penetration, the lateral friction on the pile material becomes greater, as does the mass of the earth which moves along with it. In this case, greater energy pulses are more effective. The necessary driving depth can usually not be reached at all without impact, or the vibratory equipment takes on considerable dimensions, and the required power can amount to hundreds of kilowatts. Driving can better be carried out in friable ground by means of vibration, in cohesive ground by means of impact or impact-vibration. The power utilized is not optimally exploited. At a shallow depth of penetration and high amplitude, the whole arrangement tends to jump, penetration is slight, power consumption is low. At greater depths of penetration, the energy requirement often increases unpredictably, which leads to overloading of the drive facilities and can cause damage to the mechanical structure of the pile driver.
It is an object of this invention to provide an improved pile driver and extractor which makes it possible to save very considerably on energy.
To this end, in the driving and extracting apparatus according to the present invention, of the type initially mentioned, the reaction mass has drive and spring cylinders into which drive and spring pistons extend, the drive cylinder being connected to a pulsator, and the spring cylinder being connected to a pneumatic spring.